November '15

For the Business of Apparel Decorating

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76 || P R I N T W E A R N O V E M B E R 2 0 1 5 under-bases must not penetrate excessively; most colors will do just that and not offer a substantial foundation for any overprint color. Also note that very few colors are built to flash rapidly and the lev- el of hot tack of most colors will surely glue the sub- sequent screen to itself. In consideration, the bal- ance of this section will deal with flash-capable inks. Ever notice if we meter the under-base too thin it doesn't quite get it in the finished product, but when we meter the under-base too thick it doesn't quite get it either? The key parameter for a quality under-base ink is matte-down—the ability of the ink to cover all garment fibers irrespective of the thickness of deposit. If you walked out into production and asked the top press operator "How do we achieve matte- down?" they won't know because they can't know; matte-down is a result of the rheology—think total fluid and flow properties—of a high-speed ink. Matte-down using whatever mechanical means or plastisol ink at your disposal eliminates fibrilla- tion for a smooth deposit. And if via mesh, stencil, blade, and tenacity we have a smooth surface, it must be electron rich or we won't be able to print over the top of it. This is why deposit balances on the head of a pin; a tad too thin—e.g. more absor- bent shirt less electron starved ink—and we may lose the required opacity. A tad too thick and we find opacity only to have too little absorbency in the shirt to print upon. "Flash-curing" implies the temperature of the plas- tisol is elevated to a point at which the resin has ab- sorbed sufficient plasticizer and the ink is no longer fluid. The gelation process is one of sufficient tem- perature, but it takes printers some time to achieve the requisite temp. Use an IR probe or a gloss meter to define gel state per deposit, per ink. BE CAREFUL Confirmation bias is an all too human tendency to decide what the outcome of the test should be and then adapt the test parameters to prove our prior po- sition correct. For this group, often overheard to have said, "That's what I thought," we have a few caveats. First, some printers rely on Dyne pens to gauge the imprintability of the under-base, but we must be cau- tious; the solvents in the Dyne pens are liquids and are likely to flux the gelled ink to give us a false pos- itive. Plus, there is no number to gauge the holdout of an overprint color which has been printed on an under-base. Second, when we flash "water-based" inks, we must see to it their solvent fumes are properly exhausted without filtering through the operator and the shop. Further, some plastisol inks contain VOCs and should be handled similarly on-press. Third, if you are printing a PET-bearing garment, consider the flash as an extension of your dryer— measure and be consciously aware of the delta tem- perature which will be even further beyond the level of dye sublimation. Fourth, of the three commonplace gauges of tem- perature—tapes, doughnuts, and IR probes—the third is the most recommended. The tolerances of tapes are suspect under an IR emitter for short bursts of time, and the doughnut does not react sufficiently fast. These two will give a number but not one we should rely upon. Overall, flashing is a delicate process that takes much patience and testing. To make it even more difficult, it is forever changing. However, with a lit- tle careful consideration of all the components that effect the final print, there is no reason we can't get close to mastering this process and profit from the pain it causes. FLASH-CURE TROUBLESHOOTING ISSUE WITH INK LAY-DOWN MESH ADJUSTMENT Not smooth and deposit too thin Next larger thread diameter and drop 2-counts Not smooth and deposit acceptable Keep the thread diameter and drop 1-count Not smooth and deposit too thick Keep the count but drop 1-thread diameter BLADE & PRINT PROBLEM ON-PRESS ADJUSTMENT Platen deflection, not smooth but clearing Reduce blade angle & pressure Platen deflection, not smooth, clearing front only Calibrate press/replace blade Platen deflection, not smooth, not clearing [global] Raise flood-bar and increase gap

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